Image forming apparatus with mirror curving adjustment unit

ABSTRACT

An image forming apparatus according to an embodiment includes a photoconductive drum, a light scanning unit, a reflection mirror, a support member, and a cam. The light scanning unit forms a light scanning beam with which the photoconductive drum is irradiated. The reflection mirror guides the light scanning beam toward the photoconductive drum. The support member supports both ends of the reflection mirror in a longitudinal direction. The cam is provided in the support member. The cam comes into contact with the reflection mirror in an intermediate portion of the reflection mirror in the longitudinal direction. The cam moves the intermediate portion in a plate thickness direction of the reflection mirror with respect to a support position by the support member.

FIELD

Embodiments described herein relate generally to an image formingapparatus.

BACKGROUND

There are image forming apparatuses that form images by color toner. Theimage forming apparatuses irradiate photoconductive drums with lightscanning beams. The image forming apparatuses form electrostatic latentimages on the photoconductive drums. The image forming apparatusesdevelop the electrostatic latent images to form toner images.

For example, an image forming apparatus includes a plurality ofphotoconductive drums. The image forming apparatus irradiates each ofthe photoconductive drums with a light scanning beam. It is necessary toaccurately position relative positions of the toner images on thephotoconductive drums between the photoconductive drums. In particular,if the scanning lines of the light scanning beams are bent, imagequality deteriorates.

The bending of the scanning lines of the light scanning beams occurs dueto various component errors and arrangement errors in scanning opticalsystems. In particular, in full-color image forming apparatuses, lightscanning beams are folded using a plurality of reflection mirrors.Therefore, if the reflection surface of each reflection mirror is curveddue to a processing error, the bending of the scanning lines increases.

In the related art, to correct the bending of the scanning lines,curving amounts of reflection mirrors are adjusted in some cases. Forexample, the rear surfaces of the reflection mirrors are pressed byretractable mechanisms such as screws.

However, in such adjustment methods, the reflection mirrors are curvedonly in one direction. Further, at the time of the adjustment, a stopperis necessary so that the reflection mirrors do not exceed deformationlimits. Furthermore, since the retractable mechanisms are operated fromthe rear surfaces of the reflection mirrors toward the mirrors,operability is poor.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an example ofthe entire configuration of an image forming apparatus according to anembodiment.

FIG. 2 is a schematic diagram illustrating an example of theconfiguration of a laser scanning unit.

FIG. 3 is a schematic perspective view illustrating an example of theconfiguration of a reflection mirror.

FIG. 4 is a schematic front view illustrating an example of theconfiguration of a mirror curving adjustment unit.

FIG. 5 is a schematic diagram when viewed from B in FIG. 4.

FIG. 6 is a schematic cross-sectional diagram taken along the line C-Cin FIG. 5.

FIG. 7 is a schematic cross-sectional diagram taken along the line D-Din FIG. 5.

FIG. 8 is a schematic perspective view illustrating an example of theconfiguration of an elastic member.

FIG. 9 is a schematic cross-sectional diagram taken along the line E-Ein FIG. 5.

FIG. 10 is a schematic cross-sectional diagram taken along the line F-Fin FIG. 9.

FIG. 11A is a schematic cross-sectional view illustrating an example ofa support shape of an end portion of the reflection mirror.

FIG. 11B is a schematic cross-sectional view illustrating an example ofthe support shape of the end portion of the reflection mirror.

FIGS. 12A to 12C are schematic cross-sectional views for describing anoperation for curving adjustment of the reflection mirror.

FIG. 13 is a schematic diagram for describing an operation of adjustingthe bending of a scanning line.

FIG. 14 is a schematic cross-sectional view for describing modificationexamples.

DETAILED DESCRIPTION

An image forming apparatus according to an embodiment includes aphotoconductive drum, a light scanning unit, a reflection mirror, asupport member, and a cam. The light scanning unit forms a lightscanning beam with which the photoconductive drum is irradiated. Thereflection mirror guides the light scanning beam toward thephotoconductive drum. The support member supports both ends of thereflection mirror in a longitudinal direction. The cam is provided inthe support member. The cam comes into contact with the reflectionmirror in an intermediate portion of the reflection mirror in thelongitudinal direction. The cam moves the intermediate portion in aplate thickness direction of the reflection mirror with respect to asupport position by the support member.

Embodiment

Hereinafter, an image forming apparatus 100 according to an embodimentwill be described with reference to the drawings. In the drawings, thesame reference numerals are given to the same configurations unlessotherwise stated.

FIG. 1 is a schematic cross-sectional view illustrating an example ofthe entire configuration of an image forming apparatus according to anembodiment. FIG. 2 is a schematic diagram illustrating an example of theconfiguration of a laser scanning unit of the image forming apparatusaccording to the embodiment. FIG. 3 is a schematic perspective viewillustrating an example of the configuration of a reflection mirror ofthe image forming apparatus according to the embodiment. FIG. 4 is aschematic front view illustrating an example of the configuration of amirror curving adjustment unit of the image forming apparatus accordingto the embodiment. FIG. 5 is a schematic diagram when viewed from B inFIG. 4. FIG. 6 is a schematic cross-sectional diagram taken along theline C-C in FIG. 5. FIG. 7 is a schematic cross-sectional diagram takenalong the line D-D in FIG. 5. FIG. 8 is a schematic perspective viewillustrating an example of an elastic member of the image formingapparatus according to the embodiment. FIG. 9 is a schematiccross-sectional diagram taken along the line E-E in FIG. 5. FIG. 10 is aschematic cross-sectional diagram taken along the line F-F in FIG. 9.FIG. 11A is a schematic cross-sectional view illustrating an example ofa support shape of an end portion of the reflection mirror of the imageforming apparatus according to the embodiment. FIG. 11B is a schematiccross-sectional view illustrating an example of the support shape of theend portion of the reflection mirror of the image forming apparatusaccording to the embodiment.

As illustrated in FIG. 1, the image forming apparatus 100 according tothe embodiment includes a control panel 1, a scanner unit 2, a printerunit 3, a sheet supply unit 4, a carrying unit 5, and a control unit 6.

The control panel 1 operates the image forming apparatus 100 when anoperator performs an operation.

The scanner unit 2 reads image information of a copy target asbrightness and darkness of light. The scanner unit 2 outputs the readimage information to the printer unit 3.

The printer unit 3 forms an output image (hereinafter referred to as atoner image) by a developer including toner or the like based on theimage information read by the scanner unit 2 or image information fromthe outside.

The printer unit 3 transfers the toner image to the surface of a sheetS. The printer unit 3 applies heat and pressure to the toner image onthe surface of the sheet S to fix the toner image onto the sheet S.

The sheet supply unit 4 supplies sheets S to the printer unit 3 one byone at a timing at which the printer unit 3 forms the toner image. Thesheet supply unit 4 includes a plurality of sheet feeding cassettes 20Aand 20B. Each of the sheet feeding cassettes 20A and 20B accommodatesthe sheets S of sizes and kinds set in advance. The sheet feedingcassettes 20A and 20B include pickup rollers 21A and 21B and sheetfeeding rollers 22A and 22B, respectively. The pickup rollers 21A and21B respectively pick up the sheets S one by one from the sheet feedingcassettes 20A and 20B. The picked-up sheets S are moved to the carryingunit 5 by the respective sheet feeding rollers 22A and 22B.

The carrying unit 5 includes carrying rollers 23 and resist rollers 24.The carrying unit 5 carries the sheet S supplied from the sheet supplyunit 4 to the resist rollers 24. The resist rollers 24 carry the sheet Sat a timing at which the printer unit 3 transfers the toner image to thesheet S.

The carrying rollers 23 abuts the front end of the sheet S in a carryingdirection to a nip N of the resist rollers 24. The carrying rollers 23arrange the position of the front end of the sheet S in the carryingdirection by bending the sheet S.

The resist rollers 24 match the front end of the sheet S in the nip N.Further, the resist rollers 24 carry the sheet S toward a transfer unit28 to be described below.

Next, the detailed configuration of the printer unit 3 will bedescribed.

The printer unit 3 includes image forming units 25Y, 25M, 25C, and 25K,a laser scanning unit 26, an intermediate transfer belt 27, the transferunit 28, a fixing unit 29, and a transfer belt cleaning unit 31.

Each of the image forming units 25Y, 25M, 25C, and 25K forms the tonerimage on the intermediate transfer belt 27.

As illustrated in FIG. 2, the image forming units 25Y, 25M, 25C, and 25Kinclude photoconductive drums 25 y, 25 m, 25 c, and 25 k, respectively.The image forming units 25Y, 25M, 25C, and 25K form the toner images ofyellow, magenta, cyan, and black on the photoconductive drums 25 y, 25m, 25 c, and 25 k.

The photoconductive drums 25 y, 25 m, 25 c, and 25 k are disposed inparallel with spaces therebetween. Central axis lines of thephotoconductive drums 25 y, 25 m, 25 c, and 25 k are disposed on thesame horizontal surface. The central axis lines of the photoconductivedrums 25 y, 25 m, 25 c, and 25 k are perpendicular to the carryingdirection of the sheet S in the printer unit 3.

As illustrated in FIG. 1, a known charging unit, a known developingunit, a known transfer roller, a known cleaning unit, and a knowndischarging unit are disposed around each of the photoconductive drums25 y, 25 m, 25 c, and 25 k. The transfer roller faces thephotoconductive drum. The intermediate transfer belt 27 to be describedbelow is nipped between the transfer roller and the photoconductivedrum. The laser scanning unit 26 is disposed below the charging unit andthe developing unit.

As illustrated in FIG. 2, the laser scanning unit 26 irradiates thesurfaces of the photoconductive drums 25 y, 25 m, 25 c, and 25 k withlaser beams L1, L2, L3, and L4 (laser scanning beam). Image informationof yellow, magenta, cyan, and black is supplied to the laser scanningunit 26.

The laser beams L1, L2, L3, and L4 are modulated based on the imageinformation of yellow, magenta, cyan, and black.

On the surfaces of the photoconductive drums 25 y, 25 m, 25 c, and 25 k,the laser beams L1, L2, L3, and L4 are scanned to lines extending in thelongitudinal directions of the photoconductive drums 25 y, 25 m, 25 c,and 25 k.

The scanning lines of the laser beams L1, L2, L3, and L4 become straightlines if there is no component error and assembly error in the laserscanning unit 26. However, the laser scanning unit 26 has a componenterror and an assembly error. For this reason, the scanning lines of thelaser beams L1, L2, L3, and L4 are deviated from target straight lines.If the scanning lines are not parallel to the target straight lines,adjusting slopes of the scanning lines to be described below isperformed at the time of assembly. Further, the scanning lines are bentwith respect to the target straight lines in some cases. In contrast, inthe image forming apparatus 100 according to the embodiment, adjustingbending of the scanning lines to be described below is performed at thetime of the assembly.

After the scanning lines are adjusted, the laser beams L1, L2, L3, andL4 become parallel to the target straight lines. The parallel deviationin the target straight lines is corrected by controlling a timing atwhich a latent image is formed.

Exposure portions of the laser beams L1, L2, L3, and L4 on the surfacesof the photoconductive drums 25 y, 25 m, 25 c, and 25 k are discharged.The laser beams L1, L2, L3, and L4 form electrostatic latent images onthe surfaces of the photoconductive drums 25 y, 25 m, 25 c, and 25 kaccording to the image information.

The laser scanning unit 26 includes a housing 40, a laser light source(not illustrated), and a writing optical system 60.

Hereinafter, a direction in which a vertical line extends is referred toas a Z direction in the laser scanning unit 26 in the dispositionaccording to the embodiment. In the Z direction, an upward verticaldirection is referred to as a Z+ direction and a downward verticaldirection is referred to as a Z− direction in some cases. A directionperpendicular to the central axis line of each of the photoconductivedrums 25 y, 25 m, 25 c, and 25 k on the horizontal surface perpendicularin the Z direction is referred to as an X direction. In the X direction,a direction directed from the photoconductive drum 25 y to thephotoconductive drum 25 k is referred to as an X+ direction and adirection directed from the photoconductive drum 25 k to thephotoconductive drum 25 y is referred to as an X− direction in somecases. A direction perpendicular to the Z and X directions is referredto as a Y direction. In the Y direction, a direction directed to therear side illustrated in the drawing is referred to as a Y+ directionand a direction directed to the front direction illustrated in thedrawing is referred to as a Y− direction in some cases.

The housing 40 fixes the laser light source (not illustrated) and thewriting optical system 60 in a definite positional relation. The housing40 is covered with a cover (not illustrated). An opening through whichthe laser beams L1, L2, L3, and L4 transmit is formed in the covercovering the upper portion of the housing 40.

The laser light source includes four laser diodes (hereinafter referredto as LDs), driving circuits of the LDs, and a collimator lens. Thelaser light generated in the laser light source is turned to a parallelbeam by the collimator lens. The laser light source is fixed to a sidesurface of the housing 40.

The writing optical system 60 includes a cylindrical lens (notillustrated), a polygon motor 41, a fθ lens 42, and a plurality ofreflection mirrors. The polygon motor 41 and the fθ lens 42 form a lightscanning unit that forms a light scanning beam with which thephotoconductive drum is irradiated.

Hereinafter, the configuration of the writing optical system 60 will bedescribed along an optical path of each laser beam.

Hereinafter, when a direction on a cross-sectional surface perpendicularto the optical axis of each laser beam is described, a main scanningdirection and a sub-scanning direction are used in some cases. The mainscanning direction is a direction in which the laser beam is movedthrough rotation of a polygon mirror 41 a to be described below. Thesub-scanning direction is a direction perpendicular to the main scanningdirection.

The cylindrical lens forms each laser beam from the laser light sourceon the polygon mirror 41 a to be described below in the sub-scanningdirection. The cylindrical lens is disposed between the laser lightsource and the polygon motor 41.

The polygon motor 41 scans each laser beam in a deflection manner. Thepolygon motor 41 rotates a rotor 41 b. The polygon mirror 41 a is fixedto the rotor 41 b.

The polygon mirror 41 a has a plurality of deflection surfaces atpositions of an equal distance from a rotation axis line O of the rotor41 b. The plurality of deflection surfaces are disposed in a polygonalform when viewed in the direction directed along the rotation axis lineO. A DC motor can be used as the polygon motor 41.

In the embodiment, one polygon motor 41 is used. The polygon motor 41reflects the laser beams L1, L2, L3, and L4 at the same position whenviewed in the Z direction. Therefore, all of the laser beams L1, L2, L3,and L4 are scanned in the deflection manner in the same direction whenviewed in the Z direction. The rotation axis line of the polygon mirror41 a extends in the Z direction.

The polygon motor 41 is fixed at a position deviated from the center ofthe housing 40 in the X+ direction.

When the laser beams L1, L2, L3, and L4 are reflected from the polygonmirror 41 a, the laser beams L1, L2, L3, and L4 diverge in thesub-scanning direction.

The fθ lens 42 forms the laser beams L1, L2, L3, and L4 reflected fromthe polygon mirror 41 a on the photoconductive drums 25 y, 25 m, 25 c,and 25 k, respectively. The fθ lens 42 has fθ characteristics.Therefore, the fθ lens 42 scans the laser beams L1, L2, L3, and L4scanned equiangularly by the polygon motor 41 to image surfaces at thesame speed.

The fθ lens 42 is located in the X− direction from the polygon motor 41.The fθ lens 42 according to the embodiment includes a first lens 42A anda second lens 42B in order from the polygon motor 41.

The first lens 42A causes the laser beams L1, L2, L3, and L4 incident onthe polygon mirror 41 a at different positions in the Z direction to beincident.

The second lens 42B further condenses the laser beam L1 condensed by thefirst lens 42A. The laser beams L1, L2, L3, and L4 transmitting throughthe second lens 42B scan the image surfaces at the same speed throughrotation of the polygon mirror 41 a. The optical axes of the laser beamsL1, L2, L3, and L4 transmitting through the second lens 42B arealienated from each other in parallel in the Z direction.

The plurality of reflection mirrors in the writing optical system 60reflect the laser beams L1, L2, L3, and L4 transmitting through the fθlens 42. The plurality of reflection mirrors in the writing opticalsystem 60 fold the optical paths of the laser beams L1, L2, L3, and L4.The plurality of reflection mirrors in the writing optical system 60guide the laser beam L4 to each of the surfaces of the photoconductivedrums 25 y, 25 m, 25 c, and 25 k.

The plurality of mirrors of the writing optical system 60 include firstmirrors 43 y, 43 m, 43 c, and 43 k, second mirrors 44 m, 44 c, and 44 k,and third mirrors 45 m, 45 c, and 45 k. The plurality of mirrors of thewriting optical system 60 are all formed of long and thin rectangularglass plates of which reflection surfaces are formed on the externalsurfaces. The longitudinal directions of the plurality of mirrorsarranged in the writing optical system 60 are all matched in the Ydirection.

The first mirror 43 y is located in the X− direction from the secondlens 42B. The first mirror 43 y upward reflects only the laser beam L1emitted from the second lens 42B. The first mirror 43 y guides the laserbeam L1 to the surface of the photoconductive drum 25 y.

The first mirror 43 m, the second mirror 44 m, and the third mirror 45 mreflect the laser beam L2 emitted from the second lens 42B in sequenceand guide the laser beam L2 to the surface of the photoconductive drum25 m.

The first mirror 43 m is located in the X− direction from the secondlens 42B. The first mirror 43 m is located in the X+ direction from thefirst mirror 43 y. The first mirror 43 m upward reflects only the laserbeam L2 emitted from the second lens 42B.

The second mirror 44 m is located above the first mirror 43 y. Thesecond mirror 44 m reflects the laser beam L2 reflected from the firstmirror 43 m in the X+ direction.

The third mirror 45 m is located in the X+ direction from the secondmirror 44 m. The third mirror 45 m reflects the laser beam L2 reflectedfrom the second mirror 44 m toward the surface of the photoconductivedrum 25 m.

The first mirror 43 c, the second mirror 44 c, and the third mirror 45 creflect the laser beam L3 emitted from the second lens 42B in sequenceand guide to the surface of the photoconductive drum 25 c.

The first mirror 43 c is located in the X− direction from the secondlens 42B. The first mirror 43 c is located in the X+ direction from thefirst mirror 43 m. The first mirror 43 c upward reflects only the laserbeam L3 emitted from the second lens 42B.

The second mirror 44 c is located above the first mirror 43 c. Thesecond mirror 44 c reflects the laser beam L3 reflected from the firstmirror 43 c in the X+ direction.

The third mirror 45 c is located in the X+ direction from the secondmirror 44 c. The third mirror 45 c reflects the laser beam L3 reflectedfrom the second mirror 44 c toward the surface of the photoconductivedrum 25 c.

The first mirror 43 k, the second mirror 44 k, and the third mirror 45 kreflect the laser beam L4 emitted from the second lens 42B in sequenceand guide the laser beam L4 to the surface of the photoconductive drum25 k.

The first mirror 43 k is located in the X− direction from the secondlens 42B. The first mirror 43 k is located in the X+ direction from thefirst mirror 43 c. The first mirror 43 k upward reflects only the laserbeam L4 emitted from the second lens 42B.

The second mirror 44 k is located above the first mirror 43 k. Thesecond mirror 44 k reflects the laser beam L4 reflected from the firstmirror 43 k in the X+ direction.

The third mirror 45 k is located in the X+ direction from the secondmirror 44 k. The third mirror 45 k reflects the laser beam L4 reflectedfrom the second mirror 44 k toward the surface of the photoconductivedrum 25 k.

A dust-proof glass 46 is disposed on an optical path between the firstmirror 43 y and the photoconductive drum 25 y. Likewise, the dust-proofglass 46 is also disposed along each of an optical path between thethird mirror 45 m and the photoconductive drum 25 m, an optical pathbetween the third mirror 45 c and the photoconductive drum 25 c, and anoptical path between the third mirror 45 k and the photoconductive drum25 k.

The dust-proof glasses 46 fill four openings (not illustrated) coveringthe upper portion of the housing 40.

The laser scanning unit 26 adjusts the bending of the scanning lineusing the first mirror 43 y and the third mirrors 45 m, 45 c, and 45 k.The first mirror 43 y and the third mirrors 45 m, 45 c, and 45 k arereflection mirrors that reflect the laser beams L1, L2, L3, and L4toward the immediate fronts of the photoconductive drums 25 y, 25 m, 25c, and 25 k along the optical path.

A mirror curving adjustment unit 50 is provided in each of the firstmirror 43 y and the third mirrors 45 m, 45 c, and 45 k.

The mirror curving adjustment units 50 have the same configuration.Hereinafter, the configuration of the mirror curving adjustment unit 50will be described exemplifying a case in which the mirror curvingadjustment unit 50 is provided in the first mirror 43 y.

As illustrated in FIG. 3, the mirror curving adjustment unit 50 includesa support member 51, end pressure members 53, an adjustment unitpressure member 52, and a cam 56.

The support member 51 supports a first end E1 and a second end E2 of thefirst mirror 43 y. The support member 51 has higher rigidity than thefirst mirror 43 y.

As illustrated in FIGS. 4 and 5, the support member 51 is a channelmaterial including a bottom surface portion 51 b and side surfaceportions 51 c and 51 d.

The bottom surface portion 51 b is a flat portion that covers a rearsurface Mb of a reflection surface Ma of the first mirror 43 y in thelongitudinal direction. The length of the bottom surface portion 51 b inthe longitudinal direction is shorter than the length of the firstmirror 43 y in the longitudinal direction. The width of the bottomsurface portion 51 b in the transverse direction is wider than the width(a width between the side surfaces Mc and Md) of the first mirror 43 yin the transverse direction.

At the end of the support member 51 in the longitudinal direction, anend that supports the first end E1 of the first mirror 43 y is referredto as a first end e1. At the end of the support member 51, an end thatsupports the second end E2 of the first mirror 43 y is referred to as asecond end e2.

The side surface portions 51 c and 51 d are flat portions bent from theend of the bottom surface portion 51 b in the transverse direction inthe range of the entire length of the bottom surface portion 51 b. Theside surface portions 51 c and 51 d can be bent in the same directionwith respect to the bottom surface portion 51 b. The side surfaceportions 51 c and 51 d can be bent at right angles to the bottom surfaceportion 51 b. The surface of the bottom surface portion 51 b on theinside of the bending of the side surface portions 51 c and 51 d isreferred to as an surface 51 a (see FIG. 3)

A support protrusion 51 e protrudes in the same direction as the sidesurface portions 51 c and 51 d from the surface 51 a of the first end e1of the bottom surface portion 51 b. A support protrusion 51 f protrudesin the same direction as the side surface portions 51 c and 51 d fromthe surface 51 a of the second end e2 of the bottom surface portion 51b. Both of the protrusion heights of the support protrusions 51 e and 51f from the surface 51 a are h. The protrusion height h is sufficientlygreater than a curving adjustment amount of the first mirror 43 y. Thefirst mirror 43 y is curved through the adjustment of the bending of thescanning line to be described below. However, even when the first mirror43 y is curved, the rear surface Mb of the first mirror 43 y does notcome into contact with the bottom surface portion 51 b.

The support protrusions 51 e and 51 f support the first mirror 43 y onthe rear surface Mb. The rear surface Mb of the first mirror 43 y issupported at two points by the support protrusions 51 e and 51 f.

The side surface portions 51 c and 51 d protrude from the reflectionsurface Ma of the first mirror 43 y supported by the support member 51.

As illustrated in FIG. 6, a notch portion 51 g is formed in the sidesurface portion 51 d at the first end e1 of the support member 51.

The notch portion 51 g lowers the height of the side surface portion 51d with respect to the bottom surface portion 51 b. The height from thebottom surface portion 51 b to the notch portion 51 g is lower than thereflection surface Ma of the first mirror 43 y supported by the supportprotrusion 51 e. The width of the notch portion 51 g is a width intowhich the second pressure member 53 to be described below can beinserted. The notch portion 51 g is formed at a position overlapping theprotrusion position of the support protrusion 51 e in the longitudinaldirection of the side surface portion 51 d.

As illustrated in FIG. 7, a notch portion 51 h is formed in the sidesurface portion 51 d at the second end e2 of the support member 51. Thenotch portion 51 h lowers the height of the side surface portion 51 dwith respect to the bottom surface portion 51 b. The height from thebottom surface portion 51 b to the notch portion 51 h is lower than thereflection surface Ma of the first mirror 43 y supported by the supportprotrusion 51 f. The width of the notch portion 51 h is the same as thewidth of the notch portion 51 g. The notch portion 51 h is formed in thelongitudinal direction of the side surface portion 51 d in a rangeoverlapping with the protrusion position of the support protrusion 51 f.

As indicated by a dotted line in FIG. 4, the same notch portions 51 gand 51 h as those of the side surface portion 51 d are formed in theside surface portion 51 c at the first end e1 and the second end e2 ofthe support member 51. The notch portions 51 g and 51 h are formed atpositions facing each other with the bottom surface portion 51 b nippedtherebetween.

As illustrated in FIG. 8, a hole portion 51 p penetrating through thebottom surface portion 51 b is formed at the center of the supportmember 51 in the longitudinal direction. A cam support plate portion 51i extends from the side surface portion 51 c on the outside of the holeportion 51 p. The cam support plate portion 51 i protrudes from thebottom surface portion 51 b. The cam support plate portion 51 iprotrudes on the opposite side to the protrusion direction of the sidesurface portion 51 c. A bearing hole 51 n that rotatably supports a cam56 to be described below is provided in the cam support plate portion 51i. The center of the bearing hole 51 n is located at a position of adistance d from the surface 51 a of the bottom surface portion 51 b.

A notch portion 51 k is formed at the end of the side surface portion 51c in the protrusion direction.

The notch portion 51 k lowers the height of the side surface portion 51c with respect to the bottom surface portion 51 b. A height from thesurface 51 a to the notch portion 51 k is lower than the reflectionsurface Ma of the first mirror 43 y supported by the support protrusions51 e and 51 f. Further, the height from the surface 51 a to the notchportion 51 k is lower than the reflection surface Ma of the first mirror43 y even when the first mirror 43 y is curved within the adjustmentrange.

The width of the notch portion 51 k is a width into which the adjustmentunit pressure member 52 to be described below can be inserted. The notchportion 51 k is formed in a range wider than the width of the holeportion 52 p of the adjustment unit pressure member 52 in thelongitudinal direction of the support member 51.

A locking protrusion 51 m stopping the adjustment unit pressure member52 to be described below protrudes inside the notch portion 51 k.

As illustrated in FIG. 9, a cam support plate portion 51 j extends fromthe side surface portion 51 d on the outside of the hole portion 51 p.The cam support plate portion 51 j protrudes from the bottom surfaceportion 51 b. The cam support plate portion 51 j protrudes on theopposite side to the protrusion direction of the side surface portion 51d. A bearing hole 51 r that rotatably supports the cam 56 to bedescribed below is provided in the cam support plate portion 51 j. Thebearing hole 51 r is an oval hole long in the protrusion direction ofthe cam support plate portion 51 j. In the bearing hole 51 r, the centerof a circular arc portion in the protrusion direction of the cam supportplate portion 51 j is located at the distance d from the surface 51 a ofthe bottom surface portion 51 b.

The same notch portion 51 k as that of the side surface portion 51 c isformed at the end of the side surface portion 51 d in the protrusiondirection.

As illustrated in FIGS. 6 and 7, the end pressure members 53 press thefirst mirror 43 y toward the support protrusions 51 e and 51 f. One endpressure member 53 is disposed at each of the first end e1 and thesecond end e2 of the support member 51. The end pressure member 53 atthe first end e1 locks in the notch portion 51 g of the support member51. The end pressure member 53 at the second end e2 locks in the notchportion 51 h of the support member 51.

The end pressure members 53 are formed of appropriate elastic members.For example, the end pressure members 53 are formed by folding a metalthin plate with an excellent spring property.

Hereinafter, the configuration of each end pressure member 53 will bedescribed. This description is based on a positional relation in whichthe end pressure member 53 is mounted on the first end e1 (the secondend e2) of the support member 51.

The end pressure member 53 includes a base portion 53 a, a side plateportion 53 b, a mirror pressure portion 53 c, a guide portion 53 d, aspring portion 53 e, and a side surface pressure portion 53 f (see FIG.5)

The base portion 53 a has a rectangular plate shape. The width of thebase portion 53 a in the transverse direction is substantially the sameas the width of the support member 51 in the transverse direction. Thebase portion 53 a faces the bottom surface portion 51 b of the supportmember 51 in the opposite direction to the protrusion direction of theside surface portions 51 c and 51 d.

The side plate portion 53 b is a plate-shaped portion that rises atright angles from the end of the base portion 53 a in the transversedirection. As illustrated in FIG. 5, the side plate portions 53 b faceeach other with the first mirror 43 y nipped therebetween. Hereinafter,a region between the side plate portions 53 b is referred to as aninside of the side plate portions 53 b.

The side plate portions 53 b nip the side surface portions 51 c and 51 dof the support member 51. In the side plate portions 53 b, there is agap between the side surface portions 51 c and 51 d. The side plateportions 53 b can move in the protrusion direction of the side surfaceportions 51 c and 51 d.

As illustrated in FIGS. 6 and 7, the mirror pressure portion 53 c isformed in a flake shape. The mirror pressure portion 53 c protrudes tothe inside of the side plate portion 53 b at the front end of each sideplate portion 53 b in the protrusion direction. A distance from the baseportion 53 a to each mirror pressure portion 53 c is longer than adistance from the bottom surface portion 51 b of the support member 51to the reflection surface Ma of the first mirror 43 y.

The mirror pressure portions 53 c are located above the side surfaceportions 51 c and 51 d in the notch portions 51 g and 51 h of thesupport member 51. The mirror pressure portions 53 c overlap with aneffective reflection region (not illustrated) on the reflection surfaceMa of the first mirror 43 y (see FIG. 5)

The mirror pressure portion 53 c of the end pressure member 53 disposedat the first end e1 nips the first mirror 43 y with the supportprotrusion 51 e (see FIG. 6). The mirror pressure portion 53 c of theend pressure member 53 disposed at the second end e2 nips the firstmirror 43 y with the support protrusion 51 f (see FIG. 7).

The guide portion 53 d is adjacent to each mirror pressure portion 53 cat the front end of the side plate portion 53 b in the protrusiondirection. Each guide portion 53 d can be bent to the inside of the sideplate portion 53 b toward the base portion 53 a.

As illustrated in FIG. 6, each guide portion 53 d at the first end e1 isfolded at upward each notch portion 51 g. Further, the guide portion 53d at the first end e1 nips the side surface portions 51 c and 51 d beloweach notch portion 51 g with the side plate portion 53 b.

As illustrated in FIG. 7, each guide portion 53 d at the second end e2is folded at upward each notch portion 51 h. Further, the guide portion53 d at the second end e2 nips the side surface portions 51 c and 51 dbelow each notch portion 51 h with the side plate portion 53 b.

As illustrated in FIGS. 6 and 7, the spring portion 53 e extends fromboth ends of the base portion 53 a in the longitudinal direction of thefirst mirror 43 y. The spring portion 53 e is curved in a U shape towardthe inside of each side plate portion 53 b. The spring portion 53 eforms a plate spring. When the spring portion 53 e is warped toward thebase portion 53 a, an elastic restoring force is generated. The frontend of the spring portion 53 e presses the bottom surface portion 51 bfacing the base portion 53 a. The spring portion 53 e at the first ende1 presses the bottom surface portion 51 b on the rear side of thesupport protrusion 51 e (see FIG. 6). The spring portion 53 e at thesecond end e2 presses the bottom surface portion 51 b on the rear sideof the support protrusion 51 f (see FIG. 7).

As illustrated in FIGS. 4 and 5, the side surface pressure portion 53 fhas a protruding shape. The side surface pressure portion 53 f protrudesfrom each side plate portion 53 b in the longitudinal direction of thefirst mirror 43 y. Each side surface pressure portion 53 f has aprotrusion protruding to the inside of the side plate portion 53 b. Theprotrusions of the side surface pressure portions 53 f presses the sidesurface portions 51 c and 51 d. Therefore, the side surface portions 51c and 51 d are nipped by the side surface pressure portions 53 f.

As illustrated in FIGS. 8 and 9, the adjustment unit pressure member 52pressures the first mirror 43 y supported by the support protrusions 51e and 51 f against the cam 56 to be described below. The adjustment unitpressure member 52 pressures the intermediate portion of the firstmirror 43 y in the longitudinal direction. The adjustment unit pressuremember 52 locks in the notch portion 51 k of the support member 51.

The adjustment unit pressure member 52 is formed of an appropriateelastic member. For example, the adjustment unit pressure member 52 isformed by folding a metal thin plate with an excellent spring property.

Hereinafter, the configuration of the adjustment unit pressure member 52will be described. The description is based on a positional relation inwhich the adjustment unit pressure member 52 is mounted on the supportmember 51.

The adjustment unit pressure member 52 includes a base portion 52 a, aside plate portion 52 b, a mirror pressure portion 52 c, a guide portion52 d, a spring portion 52 e, and a ratchet pressure spring 52 g.

The base portion 52 a has a rectangular plate shape. The width of thebase portion 52 a in the transverse direction is substantially the sameas the width of the support member 51 in the transverse direction. Anotch portion 52 h is formed in the middle portion of the base portion52 a. The base portion 52 a faces the bottom surface portion 51 b of thesupport member 51 in the opposite direction to the protrusion directionof the side surface portions 51 c and 51 d.

The side plate portion 52 b is a plate-shaped portion that rises atright angles from the end of the base portion 52 a in the transversedirection. As illustrated in FIG. 5, the side plate portions 52 b faceeach other with the first mirror 43 y nipped therebetween. Hereinafter,a region between the side plate portions 52 b is referred to as aninside of the side plate portions 52 b.

As illustrated in FIG. 8, openings 52 i and 52 j are formed in themiddle portion of the side plate portions 52 b. The opening 52 i isformed at a position at which the cam support plate portion 51 i of thesupport member 51 is exposed. The opening 52 j is formed at a positionat which the cam support plate portion 51 j of the support member 51 isexposed.

A pressure plate 52 k extends inside the opening 52 j. The pressureplate 52 k tightly presses a rotational shaft portion 56 a of the cam 56to be described below against the side of the cam support plate portion51 i in the shaft direction.

The side plate portions 52 b nip the side surface portions 51 c and 51 dof the support member 51. In the side plate portions 52 b, there is agap between the side surface portions 51 c and 51 d. The side plateportions 52 b can move in the protrusion direction of the side surfaceportions 51 c and 51 d.

As illustrated in FIG. 5, the mirror pressure portion 52 c is formed ina flake shape. The mirror pressure portion 52 c protrudes to the insideof the side plate portion 52 b at the front end of each side plateportion 52 b in the protrusion direction. As illustrated in FIG. 9, adistance from the base portion 52 a to each mirror pressure portion 52 cis longer than the distance from the bottom surface portion 51 b of thesupport member 51 to the reflection surface Ma of the first mirror 43 y.

The mirror pressure portions 52 c are located above the side surfaceportions 51 c and 51 d in the notch portions 51 k of the support member51. The mirror pressure portions 52 c overlap with an effectivereflection region (not illustrated) on the reflection surface Ma of thefirst mirror 43 y (see FIG. 5).

As illustrated in FIG. 9, the guide portion 52 d is formed at the frontend of the side plate portion 52 b in the protrusion direction. Theguide portions 52 d are formed at positions at which each mirrorpressure portion 52 c is nipped (see FIG. 5). A gap in which the lockingprotrusion 51 m is entered is formed between the guide portion 52 d andthe mirror pressure portion 52 c. Each guide portion 52 d can be bent tothe inside of the side plate portion 52 b toward the base portion 52 a.

Each guide portion 52 d is folded at upward each notch portion 51 k.Further, each guide portion 52 d nips the side surface portions 51 c and51 d below each notch portion 51 k with the side plate portion 52 b.Each guide portion 52 d can nip the side surface portions 51 c and 51 din the whole range in which the first mirror 43 y moves at the time ofadjustment of the bending of the scanning line to be described below.

The spring portion 52 e extends from both ends of the base portion 52 ain the longitudinal direction of the first mirror 43 y. The springportion 52 e is curved in a U shape toward the inside of each side plateportion 52 b. The spring portion 52 e forms a plate spring. When thespring portion 52 e is warped toward the base portion 52 a, an elasticrestoring force is generated. The front end of the spring portion 52 epresses the bottom surface portion 51 b of the support member 51 facingthe base portion 52 a.

The ratchet pressure spring 52 g is a plate spring that protrudes fromthe notch portion 52 h in the longitudinal direction of the first mirror43 y. The ratchet pressure spring 52 g is folded from the base portion52 a toward the mirror pressure portion 52 c. The ratchet pressurespring 52 g nips the cam 56 to be described below with the first mirror43 y. A stopper portion 52 f protrudes at the front end of the ratchetpressure spring 52 g in the protrusion direction. The stopper portion 52f fixes the position of the cam 56 to be described below.

As illustrated in FIG. 10, the cam 56 includes the rotational shaftportion 56 a and a cam portion 56 c.

The rotational shaft portion 56 a extends along a central axis line O56.The length of the rotational shaft portion 56 a is a length traversinginside each side plate portion 52 b and each side plate portion 52 b ofthe adjustment unit pressure member 52. A first end f1 in thelongitudinal direction of the rotational shaft portion 56 a is rotatablysupported by the bearing hole 51 n of the support member 51. A secondend f2 in the longitudinal direction of the rotational shaft portion 56a is rotatably supported by the bearing hole 51 r of the support member51. The rotational shaft portion 56 a inserted through the bearing hole51 r is elastically pressed to the front side (the illustrated lowerside) of the cam support plate portion 51 j in the protrusion directionby the pressure plate 52 k of the adjustment unit pressure member 52.The rotational shaft portion 56 a is tightly pressed against thecircular arc portion of the bearing hole 51 r having the same axis ofthat of the bearing hole 51 n. The pressure plate 52 k presses therotational shaft portion 56 a even when the adjustment unit pressuremember 52 moves at the time of adjustment of the bending of the scanningline to be described below.

The central axis line O56 is parallel to the reflection surface Ma andthe rear surface Mb of the first mirror 43 y locking in each mirrorpressure portion 52 c. The central axis line O56 extends in a directionperpendicular to the longitudinal direction of the first mirror 43 y.The central axis line O56 is supported at the position of the distance dfrom the surface 51 a of the bottom surface portion 51 b.

A rotational jig engagement hole 56 b is formed inside the rotationalshaft portion 56 a on the side of the first end f1. The rotational jigengagement hole 56 b engages a rotational jig 200 that rotates the cam56. For example, when the front end of the rotational jig 200 is rotatedfrom a hexagonal bar, the rotational jig engagement hole 56 b is ahexagonal hole fitting the hexagonal bar of the rotational jig 200.

In the intermediate portion of the rotational shaft portion 56 a in thelongitudinal direction, a ratchet groove 56 d is formed at a positioncloser to the first end f1. The ratchet groove 56 d is formed along thecircumference of the same axis as the central axis line O56. The ratchetgroove 56 d extends in the axial direction of the rotational shaftportion 56 a and is formed as a concave-convex portion disposed at thesame pitch in a circumferential direction. The groove width of theratchet groove 56 d can engage with the stopper portion 52 f of theadjustment unit pressure member 52. When the stopper portion 52 f ispressed by the ratchet groove 56 d by the ratchet pressure spring 52 g,a position of the central axis line O56 of the cam 56 is fixed. However,when the cam 56 is rotated by a force exceeding a pressure force of theratchet pressure spring 52 g, the stopper portion 52 f moves on theratchet groove 56 d.

The cam portion 56 c is located in the outer circumference of therotational shaft portion 56 a to be closer to the side of the second endf2 than the ratchet groove 56 d. The cam portion 56 c has a flat shapeextending in the outer circumference direction of the rotational shaftportion 56 a. A cam surface 56 e is formed on the outer circumference ofthe cam portion 56 c. The cam portion 56 c is fixed to the rotationalshaft portion 56 a or is integrated with the rotational shaft portion 56a.

As illustrated in FIG. 9, a distance r between the cam surface 56 e andthe central axis line O56 varies in the circumferential direction. Aposition at which the distance r is a minimum value ra is indicated by apoint a. The distance r is a function of a rotational angle θ from thepoint a. The distance r has a maximum value rc (here, rc>ra) at a pointc of “θ=θc” (here, 0<θc<2π). The distance r has “rb=(ra+rc)/2” at thepoint b of “θ=θb=θc/2.”

The distance r is a linearly monotonously increasing function for theangle θ on a path reaching from the point a to the point c via the pointb. When the rotational angle θ further increases from the point c, thedistance r gradually decreases. The position returns to the point a at“θ=2π.” The distance r returns to ra at the point a.

The distance rb is assumed to be rb=h+d. As described above, h indicatesa protrusion amount of the support protrusions 51 e and 51 f. Asillustrated in FIG. 9, when the cam surface 56 e comes into contact withthe rear surface Mb at the point b, the rear surface Mb is a flatsurface that is parallel to the surface 51 a of the bottom surfaceportion 51 b. When the cam surface 56 e comes into contact with the rearsurface Mb at a position other than the point b, the first mirror 43 yreceives an external force from the cam surface 56 e to be curved.

For rc and ra, “rc−rb≦δ” and “ra−rb≦δ” are assumed to be satisfied.Here, δ is an allowable curving amount of the first mirror 43 y withrespect to support positions of the support protrusions 51 e and 51 f ofthe first mirror 43 y. The allowable curving amount is defined to be alimit of a curving amount by which the first mirror 43 y does notdamage.

As illustrated in FIGS. 4 and 5, the first mirror 43 y is inserted intothe inside of the mirror curving adjustment unit 50 having theabove-described configuration. The direction of the first mirror 43 y isa direction in which the rear surface Mb and the side surfaces Mc and Mdface the bottom surface portion 51 b and the side surface portions 51 cand 51 d of the support member 51, respectively.

The first end E1 and the second end E2 of the first mirror 43 y areexposed outward in the longitudinal direction of the support member 51.

The example of the configuration of the mirror curving adjustment unit50 was described exemplifying the first mirror 43 y.

In regard to the first mirror 43 y and the third mirrors 45 m, 45 c, and45 k, the disposition positions along the optical path are substantiallythe same as each other. The lengths of the first mirror 43 y and thethird mirrors 45 m, 45 c, and 45 k are substantially the same.Therefore, the mirror curving adjustment unit 50 is mounted on anymirror without particularly changing the dimensions. Here, when thelength of a reflection mirror on which the mirror curving adjustmentunit 50 is mounted is different, the length of the support member 51 maybe changed.

Next, methods of fixing the first mirror 43 y and the third mirrors 45m, 45 c, and 45 k on which the mirror curving adjustment unit 50 ismounted to the housing 40 will be described. Since the fixing methodsare the same, an example of the method of fixing the third mirror 45 kwill be described as an example.

The third mirror 45 k is fixed to the housing 40 at the first end E1 andthe second end E2 exposed from the support member 51.

FIGS. 11A and 11B are sectional views illustrating portions in which thethird mirror 45 k is fixed when viewed in the Y+ direction. Thesectional views of the fixed portions of the third mirror 45 m and thethird mirror 45 c are the same. The first mirror 43 y differs from thethird mirrors 45 m, 45 c, and 45 k in a slope direction. However, whenFIGS. 11A and 11B are sectional views when viewed in the Y− direction,the first mirror 43 y is completely the same.

As illustrated in FIG. 11A, for example, protrusions 40 a and 40 b forthe third mirror 45 k are formed in the housing 40. The protrusions 40 aand 40 b position the reflection surface Ma of the first end E1.

The reflection surface Ma of the third mirror 45 k comes into contactwith the protrusions 40 a and 40 b. The protrusions 40 a and 40 b decidea slope angle of the third mirror 45 k with respect to the horizontalsurface.

The third mirror 45 k is fixed to the housing 40 by a pressure spring 55pressing the rear surface Mb toward the protrusions 40 a and 40 b.

As schematically illustrated in FIG. 11B, an adjustment protrusion 40 cis disposed in the housing 40. The adjustment protrusion 40 c positionsthe reflection surface Ma of the third mirror 45 k at the second end E2.The adjustment protrusion 40 c is connected to a driving mechanism (notillustrated). The driving mechanism (not illustrated) advances orretreats the adjustment protrusion 40 c in a protrusion direction.

The reflection surface Ma of the third mirror 45 k comes into contactwith the front end of the adjustment protrusion 40 c. When theprotrusion amount of the adjustment protrusion 40 c is changed, thefixed position of the second end E2 in the X direction is changed.Therefore, by moving the adjustment protrusion 40 c, the slope of thescanning line of the laser beam L1 can be adjusted. When the adjustmentof the slope of the scanning line ends, the position of the adjustmentprotrusion 40 c is fixed.

The third mirror 45 k is fixed to the housing 40 with the slope of thescanning line of the laser beam L1 corrected.

The example of the method of fixing the third mirror 45 k to the housing40 was described. For example, the direct fixing of the third mirror 45k to the housing 40 is not requisite. For example, the protrusions 40 aand 40 b may be formed in another member fixed to the housing 40. Theconfiguration and the movement direction of the adjustment protrusion 40c are not limited to the above-described examples.

The laser scanning unit 26 was described above.

Referring back to FIG. 1, the other configuration of the image formingapparatus 100 will be continuously described.

The intermediate transfer belt 27 is formed as an endless belt. Aplurality of rollers come into contact with the inner circumferentialsurface of the intermediate transfer belt 27. The plurality of rollersapply a tensile strength to the intermediate transfer belt 27. Theintermediate transfer belt 27 is flatly tensioned. The innercircumferential surface of the intermediate transfer belt 27 comes intocontact with a support roller 28 a at one of the positions farthest inthe tensioning direction. The inner circumferential surface of theintermediate transfer belt 27 comes into contact with a transfer beltroller 32 at the other position farthest in the tensioning direction.

The support roller 28 a forms a part of the transfer unit 28 to bedescribed below. The support roller 28 a guides the intermediatetransfer belt 27 to a secondary transfer position.

The transfer belt roller 32 guides the intermediate transfer belt 27 toa cleaning position.

On the illustrated lower surface side of the intermediate transfer belt27, the image forming units 25Y, 25M, 25C, and 25K excluding thetransfer roller are disposed in this order from the transfer belt roller32 to the transfer unit 28. The image forming units 25Y, 25M, 25C, and25K are disposed with gaps therebetween in a region between the transferbelt roller 32 and the support roller 28 a.

The developing units of the image forming units 25Y, 25M, 25C, and 25Kaccommodate developers including toner of yellow, magenta, cyan, andblack. The developing units develop electrostatic latent images on thephotoconductive drums 25 y, 25 m, 25 c, and 25 k. As a result, tonerimages are formed on the photoconductive drums 25 y, 25 m, 25 c, and 25k.

The transfer rollers of the image forming units 25Y, 25M, 25C, and 25Ktransfer (primarily transfer) the toner images on the surfaces of thephotoconductive drums 25 y, 25 m, 25 c, and 25 k to the intermediatetransfer belt 27.

When the toner image reaches a primary transfer position, a transferbias is applied to each transfer roller.

The cleaning units of the image forming units 25Y, 25M, 25C, and 25Kremove the toner, for example, by scraping the toner which has not beentransferred to the surfaces of the photoconductive drums after theprimary transfer.

The discharging units of the image forming units 25Y, 25M, 25C, and 25Kirradiate the surfaces of the photoconductive drums having passedthrough the cleaning units with light. The discharging units removeelectricity of the photoconductive drums 25 y, 25 m, 25 c, and 25 k.

In the intermediate transfer belt 27, the transfer unit 28 is disposedat a position mutually adjacent to the image forming unit 25K.

The transfer unit 28 includes the support roller 28 a and a secondarytransfer roller 28 b. The secondary transfer roller 28 b and the supportroller 28 a nip the intermediate transfer belt 27. A position at whichthe secondary transfer roller 28 b and the intermediate transfer belt 27come into contact with each other is a secondary transfer position.

The transfer unit 28 transfers the toner images on the intermediatetransfer belt 27 to the surface of the sheet S at the secondary transferposition. The transfer unit 28 gives a transfer bias to the secondarytransfer position. The transfer unit 28 transfers the toner images onthe intermediate transfer belt 27 to the sheet S by the transfer bias.

The fixing unit 29 gives heat and pressure to the sheet S. The fixingunit 29 fixes the toner images transferred to the sheet S by the heatand the pressure.

The transfer belt cleaning unit 31 faces the transfer belt roller 32.The transfer belt cleaning unit 31 nips the intermediate transfer belt27. The transfer belt cleaning unit 31 scrapes the toner on the surfaceof the intermediate transfer belt 27. The transfer belt cleaning unit 31collects the scraped toner to a waste toner tank.

The printer unit 3 further includes a reversing unit 30. The reversingunit 30 reverses the sheet S discharged from the fixing unit 29 byswitchback. The reversing unit 30 carries the reversed sheet S again tothe inside of a carrying guide to the front of the resist roller 24. Thereversing unit 30 reverses the sheet S to form an image on the rearsurface of the sheet S.

The control unit 6 controls each apparatus portion of the image formingapparatus 100.

Next, an operation of the image forming apparatus 100 will be described.

In the image forming apparatus 100, an instruction to form an image isinput from the control panel 1 or the outside to the control unit 6. Thecontrol unit 6 causes the printer unit 3 to start forming an image. Theprinter unit 3 supplies the sheet S with an appropriate size from thesheet supply unit 4 to the resist roller 24.

The printer unit 3 causes the laser scanning unit 26 to form latentimages on the photoconductive drums 25 y, 25 m, 25 c, and 25 k. That is,laser light sources emit the laser beams L1, L2, L3, and L4 modulatedbased on image information.

As illustrated in FIG. 2, for example, the laser beams L1, L2, L3, andL4 are formed on the polygon mirror 41 a by the cylindrical lens (notillustrated). The laser beams L1, L2, L3, and L4 are scanned in thedeflection manner in the main scanning direction through rotation of thepolygon mirror 41 a. The laser beams L1, L2, L3, and L4 each transmitthrough the fθ lens 42 to be condensed.

The laser beam L1 is emitted from the second lens 42B, and then isreflected by the first mirror 43 y. The laser beam L1 scans the surfaceof the photoconductive drum 25 y.

The laser beam L2 (L3 or L4) is emitted from the second lens 42B, andthen is reflected by the first mirror 43 m (43 c or 43 k), the secondmirror 44 m (44 c or 44 k), and the third mirror 45 m (45 c or 45 k).The laser beam L2 (L3 or L4) scans the surface of the photoconductivedrum 25 m (25 c or 25 k).

The laser beams L1, L2, L3, and L4 scan target scanning lines if thereis no manufacturing error or no arrangement error in the opticalcomponents along the respective optical paths. However, it may bedifficult that the manufacturing error or the arrangement error in theoptical components is 0. Therefore, the scanning lines of the laserbeams L1, L2, L3, and L4 are deviated from target scanning positions.

Accordingly, in the image forming apparatus 100, adjusting the scanninglines of the laser beams L1, L2, L3, and L4 so that the scanning linesare parallel to the target scanning lines is performed when at least thelaser scanning unit 26 is assembled.

To cause the scanning lines of the laser beams L1, L2, L3, and L4 to beparallel to the target scanning lines, scanning line slopes and scanningline bending are corrected.

In the image forming apparatus 100 according to the embodiment, thescanning line slope and the scanning line bending of the laser beam L1are corrected by adjusting the curving amount and the position of thefirst mirror 43 y. In the case of the laser beams L2, L3, and L4, thepositions and the curving amounts of the third mirrors 45 m, 45 c, and45 k are adjusted instead of the first mirror 43 y.

The scanning line slope is corrected by moving the adjustment protrusion40 c, as described above. The scanning line bending is corrected usingthe mirror curving adjustment unit 50. The details of the adjustment ofthe scanning line bending using the mirror curving adjustment unit 50will be described below.

Parallel deviation of the scanning line from the target scanning line iscorrected through timing control of forming of the latent imageperformed by the control unit 6.

In this way, the electrostatic latent images corresponding to therespective image information are formed on the photoconductive drums 25y, 25 m, 25 c, and 25 k.

The developing units of the image forming units 25Y, 25M, 25C, and 25Kdevelop the respective electrostatic latent images formed on thephotoconductive drums 25 y, 25 m, 25 c, and 25 k. The toner imagescorresponding to the electrostatic latent images are formed on thesurface of the photoconductive drums 25 y, 25 m, 25 c, and 25 k.

Each toner image is primarily transferred to the intermediate transferbelt 27 by each transfer roller. At this time, a transfer timing isappropriately set according to the disposition position of each of theimage forming units 25Y, 25M, 25C, and 25K. Therefore, the toner imagesare sequentially superimposed without color deviation along with themovement of the intermediate transfer belt 27. Each toner image is sentto the transfer unit 28.

The toner image reaching the transfer unit 28 is secondarily transferredto the sheet S fed from the resist roller 24 to the transfer unit 28.The secondarily transferred toner images are fixed to the sheet S by thefixing unit 29. The sheet S to which the toner images are fixed isdischarged outside the image forming apparatus 100.

The transfer residual toner which may not be transferred to the sheet Sby the transfer unit 28 is scraped by the transfer belt cleaning unit31. The intermediate transfer belt 27 is cleaned to be reused.

The image forming on one sheet S was described above.

Next, an operation of adjusting the scanning line bending will bedescribed.

FIGS. 12A to 12C are schematic cross-sectional views for describing anoperation for curving adjustment of the reflection mirror of the imageforming apparatus according to the embodiment. FIG. 13 is a schematicdiagram for describing an operation of adjusting the bending of ascanning line in the image forming apparatus according to theembodiment.

A line width of a line image formed by the laser beams L1, L2, L3, andL4 in the main scanning direction is assumed to be Wi. In order to setcolor deviation of an image within an allowable limit, a relative linedeviation amount in the sub-scanning direction at the time of colorsuperimposition is necessarily suppressed to a value equal to or lessthan an allowable value ΔW. Even when the scanning lines have the samebending amount, bending directions are different in some cases. In thiscase, when the toner images of the corresponding scanning lines aresuperimposed, there is a concern of color deviation occurring by aboutthe maximum double of the bending amount. For this reason, in theadjustment of the scanning line bending, it is necessary to adjust thebending amount and the bending direction and reduce the line deviationamount.

As the method of adjusting the scanning line bending, the curving of thereflection surface of each reflection mirror can be considered to becorrected as a single component of the reflection mirror. The mirrorcurving adjustment unit 50 can perform such adjustment. However, in thiscase, it is necessary to provide the mirror curving adjustment units 50in all of the reflection mirrors of the writing optical system 60.

In the image forming apparatus 100 according to the embodiment, thecurving amounts of the reflection surfaces Ma of the first mirror 43 yand the third mirrors 45 m, 45 c, and 45 k are adjusted. The adjustmentamounts are decided according to the scanning line bending occurring inthe optical system closer to the light source side than the first mirror43 y and the third mirrors 45 m, 45 c, and 45 k. By adjusting thecurving amounts of the reflection surfaces Ma of the first mirror 43 yand the third mirrors 45 m, 45 c, and 45 k, the scanning line bendingoccurring in the optical system on the light source side is cancelled.The first mirror 43 y and the third mirrors 45 m, 45 c, and 45 k areforcibly curved in some cases even when the reflection surfaces Ma ofthe first mirror 43 y and the third mirrors 45 m, 45 c, and 45 k are notcurved.

First, the curving amount of the first mirror 43 y occurring due to thecam 56 will be described. For simplicity, it is assumed that thereflection surface Ma and the rear surface Mb of the first mirror 43 yin a natural state in which an external force is not applied areparallel to each other and the first mirror 43 y is not curved.

A state in which the first mirror 43 y is supported by the mirrorcurving adjustment unit 50 is schematically illustrated in FIGS. 12A to12C.

As illustrated in FIG. 12A, both ends of the first mirror 43 y in thelongitudinal direction are supported at two points of the supportprotrusions 51 e and 51 f, respectively. The third mirror 45 k istightly pressed against the support protrusions 51 e and 51 f by thespring portions 53 e.

The cam 56 comes into contact with the rear surface Mb at the point b ofthe cam surface 56 e at the time of adjustment start. The reflectionsurface Ma is pressed toward the cam 56 by the spring portion 52 e.

Specifically, as illustrated in FIG. 9, each spring portion 52 e pressesthe bottom surface portion 51 b. However, the adjustment unit pressuremember 52 is pressed in a direction separated from the bottom surfaceportion 51 b by reaction from the bottom surface portion 51 b.Therefore, a force in a direction directed to the cam 56 is applied fromthe mirror pressure portion 52 c of the adjustment unit pressure member52 to the reflection surface Ma of the first mirror 43 y.

This state is an initial state of the adjustment. In the embodiment, thefirst mirror 43 y is in the same state as the natural state in theinitial state of the adjustment.

Next, as illustrated in FIG. 10, an adjuster inserts the rotational jig200 into the rotational jig engagement hole 56 b to rotate the cam 56about the central axis line O56. For example, the adjuster rotates therotational jig 200 counterclockwise. For example, as illustrated in FIG.12B, the cam surface 56 e facing the rear surface Mb moves from thepoint b to the point a. Meanwhile, the first mirror 43 y is tightlypressed against the cam surface 56 e by the spring portion 52 e.Specifically, as illustrated in FIG. 9, the reflection surface Ma ispressed toward the cam 56 through the mirror pressure portion 52 c. Thenotch portion 51 k is formed below the mirror pressure portion 52 c.Therefore, as the distance r between the cam surface 56 e and thecentral axis line O56 decreases, the mirror pressure portion 52 c canalso move.

By doing so, the intermediate portion of the first mirror 43 y becomescloser to the central axis line O56 according to the movement of the camsurface 56 e. In contrast, the positions of both ends of the firstmirror 43 y do not move from the support protrusions 51 e and 51 f.Therefore, the first mirror 43 y is curved to be convexed downward, asillustrated in FIG. 12B. When the cam surface 56 e comes into contactwith the rear surface Mb at the point a, the first mirror 43 y isconvexed downward, as illustrated to enter a maximum curved state.However, in this case, the curving amount of the first mirror 43 y isequal to or less than an allowable curving amount of the first mirror 43y.

When the adjuster rotates the rotational jig 200 counterclockwise fromthe initial state, the first mirror 43 y is curved in the opposite wayto the above-described way. As illustrated in FIG. 12C, the first mirror43 y is curved to be convexed upward, as illustrated. When the camsurface 56 e comes into contact with the rear surface Mb at the point c,the first mirror 43 y is convexed upward, as illustrated, to enter amaximum curved state. However, in this case, the curving amount of thefirst mirror 43 y is equal to or less than the allowable curving amountof the first mirror 43 y.

Accordingly, when the cam 56 is rotated either clockwise orcounterclockwise, the first mirror 43 y is curved within the range inwhich the first mirror 43 y does not damage. The adjuster can alsorotate the cam 56 in the same direction by one circumference or more.

The adjustment of the scanning line bending is performed while measuringthe scanning line bending. In the embodiment, the first mirror 43 y andthe third mirrors 45 m, 45 c, and 45 k are fixed to the housing 40.Then, the scanning line bending is measured by scanning the laser beamsL1, L2, L3, and L4 by the polygon motor 41.

For example, FIG. 13 illustrates a state in which the third mirror 45 kis adjusted. Here, in FIG. 13, the mirror curving adjustment unit 50 isnot illustrated except for the housing 40 and the cam 56.

In the disposition state of the third mirror 45 k, the central axis lineO56 of the cam 56 extends in parallel to the reflection surface Ma inthe transverse direction of the third mirror 45 k. The rotational jigengagement hole 56 b faces a slope upper side on which the rotationaljig engagement hole 56 b advances in the X+ direction and advances inthe Z+ direction.

Therefore, the adjuster can insert the rotational jig 200 into therotational jig engagement hole 56 b from the upper side of the housing40 (not illustrated). The adjuster can easily manipulate the rotationaljig 200 from the outside of the housing 40. Since only the front end ofthe rotational jig 200 enters inside the housing 40, the rotational jig200 can be inserted without interference with the components in thehousing 40. An opening or the like for inserting the rotational jig 200may not particularly be formed in the housing 40.

Since the rotational jig 200 is located on the rear surface side of thethird mirror 45 k, the laser beam L4 is not blocked due to a rotationmanipulation of the rotational jig 200.

When the rotational jig 200 is rotated, the cam 56 is rotated withrespect to the first mirror 43 y, as described above. When the rotationof the rotational jig 200 stops, the stopper portion 52 f of the ratchetpressure spring 52 g engages with the ratchet groove 56 d so that therotational position is fixed. The third mirror 45 k is curved accordingto the rotational position of the cam portion 56 c. For example, themiddle portion of the third mirror 45 k is assumed to be moved from aposition indicated by an illustrated solid line to a position indicatedby a two-dot chain line by the cam 56. The optical path of the laserbeam L4 after the laser beam L4 is reflected from the middle portion ofthe third mirror 45 k moves in parallel in the X− direction, asindicated in an illustrated two-dot chain line. The position of thelaser beam L4 on the photoconductive drum 25 k moves from a point p0 toa point P1. A scanning line bending amount is a distance from the pointP0 to the point P1.

A rotation manipulation of the rotational jig 200 is performed whilemeasuring the scanning line bending by the curving of the third mirror45 k.

As an example of the method of measuring the scanning line bending, amethod of measuring the scanning line bending from the scanning positionof the laser beam L4 can be exemplified. In this case, the measurementcan be performed by disposing the single laser scanning unit 26 to ameasurement device. Alternatively, in the image forming apparatus 100,the measurement can be performed by disposing a measurement deviceinstead of the image forming unit 25K.

In the measurement device, a position detection sensor 201 detecting thescanning position of the laser beam L4 is disposed on an image surfaceof the laser beam L4. The position detection sensor 201 can be disposedin each of both ends and a central portion in the main scanningdirection. One position detection sensor 201 may be disposed when theposition detection sensor 201 can move in the main scanning direction. ACCD camera or the like can be adopted as the position detection sensor201.

The measurement device detects the scanning positions of at least threeseparated portions from the position detection sensors 201. Themeasurement device displays measurement results of the magnitude of thescanning line bending and a direction of the scanning line bending. Theadjuster determines a rotational direction and a rotational amount ofthe rotational jig 200 based on display of the measurement device.

The scanning line bending can also be measured in measurement in whichthe latent image on the photoconductive drum 25 k or the position of thetoner image is detected.

When the scanning line bending enters the allowable range, therotational jig 200 is removed from the cam 56. The rotation position ofthe cam 56 is maintained at a position at the time of adjustment end byengagement of the ratchet groove 56 d and the stopper portion 52 f.

Further, when there is the unadjusted reflection mirror, the sameadjustment is performed by the mirror curving adjustment unit 50 mountedon the unadjusted reflection mirror.

The scanning lines of the laser beams L1, L2, L3, and L4 can be adjustedusing one scanning line as a criterion. In this case, the scanning lineserving as the criterion is adjusted within the allowable range. Thescanning line slopes and the direction of the scanning line bending ofthe other scanning lines are adjusted to the scanning line slope and thedirection of the scanning line bending of the scanning line serving asthe criterion. In addition, the magnitude of the scanning line bendingand the scanning line slopes are adjusted so that the other scanninglines approach the scanning line serving as the criterion.

By doing so, the adjustment of the scanning lines of the laser beams L1,L2, L3, and L4 in the laser scanning unit 26 ends.

In the image forming apparatus 100, as described above, the curvingamounts and the curving directions of the first mirror 43 y and thethird mirrors 45 m, 45 c, and 45 k can be changed by the mirror curvingadjustment unit 50. Therefore, it is possible to cancel the scanningline bending by the first mirror 43 y and the third mirrors 45 m, 45 c,and 45 k and the scanning line bending occurring in the optical systemcloser to the light source side. As a result, the scanning line bendingon the photoconductive drums 25 y, 25 m, 25 c, and 25 k is suppressed.

The scanning line bending can be adjusted from the outside of thehousing 40 in a space of a narrow range on the rear surface side of theadjustment target reflection mirror. Therefore, the adjustment work canbe easily performed.

Hereinafter, modification examples of the above-described embodimentwill be described.

FIG. 14 is a schematic cross-sectional view for describing themodification examples of the image forming apparatus according to theembodiment.

In the image forming apparatus 100 having the above-describedembodiment, the central axis line O56 of the rotational shaft portion 56a of the cam 56 extends in a direction parallel to the reflectionsurface of the reflection mirror and perpendicular to the longitudinaldirection of the reflection mirror. However, the direction in which thecentral axis line O56 extends can be set to be a direction in which theadjustment is easy. For example, when the cam support plate portions 51i and 51 j are disposed in directions in which the cam support plateportions 51 i and 51 j are sloped with respect to the side surfaceportions 51 c and 51 d in the image forming apparatus 100, the directionof the central axis line O56 can be changed.

Further, the central axis line O56 may extend in parallel to thelongitudinal direction of the reflection mirror. For example, in amodification example illustrated in the main portions in FIG. 14, amirror curving adjustment unit 70 is used instead of the mirror curvingadjustment unit 50 according to the embodiment.

The mirror curving adjustment unit 70 disposes the cam 56 in parallel tothe reflection surface Ma of the third mirror 45 k with respect to thesupport member 51 and in parallel to the longitudinal direction of thethird mirror 45 k.

In such a modification example, the rotational jig 200 (not illustrated)can be inserted into the rotational jig engagement hole 56 b of the cam56 in the Y direction to adjust the scanning line bending.

In this case, even after a laser scanning unit 26 according to themodification example is mounted on the image forming apparatus 100, theadjustment is easily performed from the front side or the rear side ofthe image forming apparatus 100.

For example, in the above-described embodiment, the first mirrors 43 m,43 c, and 43 k located below the housing 40 is assumed to be adjusted.In this case, in order to perform the adjustment without blocking theoptical path, it is necessary to insert the rotational jig 200 from therear side of the housing 40. In this case, there is a concern ofworkability deteriorating when the adjustment is performed with a hand.However, when the mirror curving adjustment unit 70 is used, it is easyto perform the adjustment work easily even with a hand.

The rotational jig 200 extends along the third mirror 45 k on the sideof the rear surface of the third mirror 45 k. Therefore, for example,even in an optical path layout in which the other light scanning beamsare scanned to the upper and lower sides of the third mirror 45 k, thescanning line bending can be adjusted without blocking the other lightscanning beams.

In the above-described image forming apparatus 100, the polygon motor 41reflects the laser beams L1, L2, L3, and L4 at the same position whenviewed in the Z direction. However, the optical path layout of the laserbeams L1, L2, L3, and L4 is not limited thereto.

For example, the polygon motor 41 may have an optical path layout inwhich the laser beams L1 and L2 and the laser beams L3 and L4 aredistributed in mutually opposite directions.

In the above-described image forming apparatus 100, the example in whicheach reflection mirror adjusting the scanning line bending reflects thelight scanning beam to the immediate front of the photoconductive drumalong the optical path of each optical scanning beam was described.However, the reflection mirror on which the mirror curving adjustmentunit 50 is mounted may be a reflection mirror which is disposed onanother position.

In the above-described image forming apparatus 100, the example in whichthe cam 56 is adjusted with a hand via the rotational jig 200 wasdescribed. However, the rotational jig 200 may be configured to berotated by a motor.

According to at least one of the above-described embodiments, the imageforming apparatus includes the photoconductive drum, the light scanningunit, the reflection mirror, the support member, and the cam. In theimage forming apparatus, the intermediate portion in the longitudinaldirection of the reflection mirror of which both ends are supported bythe support members can be moved by the cam in the plate thicknessdirection. As a result, the reflection mirror is curved. In the imageforming apparatus, the scanning line bending on the photoconductive drumcan be suppressed by changing the curving amount of the reflectionmirror by the cam.

While certain embodiments have been described these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms: furthermore variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. An image forming apparatus, comprising: aphotoconductive drum; a light scanning unit that forms a light scanningbeam with which the photoconductive drum is irradiated; a reflectionmirror that guides the light scanning beam toward the photoconductivedrum; a support member that supports both ends of the reflection mirrorin a longitudinal direction; a cam that is provided in the supportmember, and comes into contact with the reflection mirror in anintermediate portion of the support member in the longitudinaldirection; a first pressure member comprising: a first elastic memberprovided on an opposite side of a reflection surface of the reflectionmirror; and a first pressing member that comes into contact with thereflection surface of the reflection mirror and presses the reflectionmirror against the support member by a force of the first elasticmember, the first pressure member being provided at a first end portionof the reflection mirror; a second pressure member comprising: a secondelastic member provided on an opposite side of the reflection surface ofthe reflection mirror; and a second pressing member that comes intocontact with the reflection surface of the reflection mirror and pressesthe reflection mirror against the support member by a force of thesecond elastic member, the second pressure member being provided at asecond end portion of the reflection mirror, the second end portionbeing provided at the opposite side of the first end portion in thelongitudinal direction; and a third pressure member comprising: a thirdelastic member provided on an opposite side of the reflection surface ofthe reflection mirror; and a third pressing member that comes intocontact with the reflection surface of the reflection mirror and pressesthe reflection mirror against the cam by a force of the third elasticmember, the third pressure member being provided at an intermediateportion of the reflection mirror.
 2. The apparatus according to claim 1,wherein the cam includes a shaft that is supported to be rotatable withrespect to the support member and a cam surface for which a distancefrom a central axis line of the shaft varies.
 3. The apparatus accordingto claim 1, further comprising: a ratchet mechanism that fixes aposition of the cam in the plate thickness direction to the supportmember.
 4. The apparatus according to claim 1, wherein a movement amountof the reflection mirror by the cam is equal to or less than anallowable deformation amount of the reflection mirror in theintermediate portion.
 5. The apparatus according to claim 1, wherein thereflection mirror reflects the light scanning beam along an optical pathof the optical scanning beam at an immediate front of thephotoconductive drum.
 6. The apparatus according to claim 2, wherein thecentral axis line of the shaft is parallel to a reflection surface ofthe reflection mirror and intersects the longitudinal direction of thereflection mirror.
 7. The apparatus according to claim 2, wherein thecentral axis line of the shaft is parallel to a reflection surface ofthe reflection mirror and is parallel to the longitudinal direction ofthe reflection mirror.
 8. The apparatus according to claim 1, whereinthe support member supports a rear surface of a reflection surface ofthe reflection mirror.
 9. The apparatus according to claim 1, wherein ata position closer to an end in the longitudinal direction than aposition at which the reflection mirror is supported by the supportmember, the reflection mirror is supported by a positioning portionregulating a positional relation with the light scanning unit.